1. Field of the Invention
This invention relates to a polishing method for chemically and mechanically polishing and flattening the surface of a substrate such as a wafer on which dielectric layers or the like are laminated in a semiconductor device manufacturing process or the like and a polishing apparatus using the same, and is suitable, for example, in a lithography process for accurately detecting the termination point of the polishing step for an insulating layer (film layer) applied onto a silicon substrate, making the film thickness of the insulating layer fall within a predetermined range and efficiently performing the process of flattening the surface configuration of the insulating layer to thereby obtain a semiconductor device of a high degree of integration.
2. Related Background Art
In recent years, along with the higher integration of semiconductor devices, making the device structure three-dimensional has advanced together with making circuit patterns minute. If the numerical aperture of a projection optical system is increased to achieve the higher integration of semiconductor devices, the depth of focus of the projection optical system will become correspondingly shallow and it will become necessary to minimize the unevenness of the surface of a substrate such as a wafer on which wiring or a dielectric is laminated, and to secure the depth of focus. Further, along with the progress of the tendency toward multiple layers, the unevenness of the surface makes the formation of wiring patterns difficult and locally results in a reduction in reliability due to the thinning of the patterns. Therefore, it is important to polish the surface of the substrate such as a wafer on which wiring or dielectric layers are laminated, remove level difference portions or uneven portions to flatten the surface, and apply a photoresist onto the flattened surface and projection-expose it to thereby achieve a high resolving power.
Also, it is an important requirement for making the irregularity of the inter-layer volume and the depth of a through hole constant to polish the insulating layer provided on a silicon substrate to thereby provide a layer of a uniform thickness.
A chemical and mechanical polishing method has heretofore been proposed as the flattening technique of removing the uneven portions or the level difference portions of the surface of a substrate such as a wafer on which wiring or dielectric layers are laminated and flattening the surface.
In the chemical and mechanical polishing, it is necessary to appropriately control the polishing rate, the slurry density in the polishing liquid, the temperature of the polished surface, etc., in order to make the polishing efficient. If there is a defect in this control, the insulating film provided on the silicon substrate will not assume a predetermined film thickness and the surface cannot be flattened, but it will become impossible to secure the depth of focus as previously mentioned or a reduction in the reliability of wiring will be caused, and a dishing phenomenon or a thinning phenomenon due to the polishing speed difference between the insulating film and the electrode wiring portion will occur, and short-circuiting between through holes will also be caused.
Therefore, when the surface of a substrate such as a wafer on which a dielectric or the like is laminated is to be polished and flattened, it becomes important to appropriately judge the termination point of polishing and flatten the surface without removing the material of the lower layer.
For example, a termination point detecting method of monitoring the film thickness and the surface configuration distribution of the surface layer of a substrate such as a wafer to be polished on which a dielectric or the like is laminated at one time on the spot and determining the level of the flattening of the whole surface or the localized flattening, and judging the optimum position for the termination of polishing becomes important in chemical and mechanical polishing. As polishing termination point detecting methods, there are, for example, a method of obtaining the amount of polishing from the polishing time, a method of obtaining a variation in polishing resistance from a variation in the electric current of a motor for driving a polishing stool, etc.
As the method of detecting the termination point of polishing in the flattening of the surface of a substrate such as a wafer on which a dielectric or the like is laminated by chemical and mechanical polishing, the method of obtaining the amount of polishing from the polishing time makes it necessary to constantly control conditions such as the pressure force to the surface to be polished, the degree of abrasion of a polishing pad, the slurry density in the polishing liquid, the temperature of the surface to be polished, etc., and therefore, it is difficult to detect the termination point accurately.
Also, the method of detecting a variation in polishing resistance from a variation in the electric current of the motor for driving a polishing stool makes it necessary to separate a signal waveform and noise from each other highly accurately and therefore, it is difficult to detect the termination point accurately and the local polishing situation of the surface to be polished cannot be detected.
On the other hand, in the step of polishing the surface of a substrate such as a wafer on which a dielectric is laminated, it becomes necessary in order to prevent the irregularity of the inter-layer volume and make the depth of a through hole constant to flatten the surface so that the surface may enter the depth of focus of the projection optical system and to make the thickness of the insulating layer on the surface fall within a predetermined range.